ExpertGPS is the best KML converter for your Garmin waypoints and tracklogs

ExpertGPS does a much better job converting Garmin GPS data to KML, because ExpertGPS creates
custom KML files for every Garmin GPS receiver, so the KML placemarks in Google Earth have the exact same icons as the
waypoints did on your GPS receiver. For example, here are the KML placemarks displayed for a Garmin GPSMAP 60CSx:

Send KML files back to your Garmin GPS

Unlike other KML converters that can't upload and download your GPS data, ExpertGPS can also
send KML directly to your Garmin GPS receiver. You can copy and paste placemarks and driving routes directly from the My Places folder in Google Earth into ExpertGPS, or use
the Import Command on the File Menu to open any KML or KMZ file. Then just click Send to GPS to send the
KML file to your Garmin GPS.